Immunological agglutination reactions are used for identifying various kinds of blood types and for detecting various kinds of antibodies and antigens in blood samples and other aqueous solutions. In a conventional procedure, a sample of red blood cells is mixed with serum or plasma in test tubes or microplates, and the mixture may then be incubated and centrifuged. Various reactions either occur or do not occur depending on, for example, the blood type of the red blood cells or whether certain antibodies are present in the blood sample. Typically, these reactions manifest themselves as clumps of cells or particles with antigens or antibodies on their surfaces, referred to as agglutinates. Thus, the absence or presence of agglutinates indicates that no reaction or a reaction has occurred, respectively, with the size and amount of agglutinates being a quantitative indicator of the level or concentration in the sample, or an indicator of the reaction strength, affinity of the complex for which the blood sample was tested.
Recently, systems have been developed in which the agglutination reaction is carried out in one portion of a vessel, and separation of agglutinated red cells is accomplished in another portion of the same vessel using a matrix which separates agglutinated cells from other components in the reagent/sample mixture. One such system is disclosed and described in U.S. Pat. Nos. 5,650,068 and 5,552,064 and are manufactured and sold by Ortho-Clinical Diagnostics Inc., Raritan, N.J., under the trademark BIOVUE. Such reaction vessels, hereinafter called “index card”, are in the form of several, usually six, columns formed in a transparent cassette with each column having an upper chamber and a lower chamber wherein the upper chamber is of a wider diameter than the lower chamber. The lower chamber contains a matrix for separating agglutinated cells from non-agglutinated cells. The diameter of the lower chamber is narrow enough such that when reagents and samples are added to the upper chamber, typically using a pipette, the reagents and samples remain in the upper chamber, and do not enter into the lower chamber, unless an additional force is applied.
In this method, gel or glass bead microparticles are contained within the lower chamber. A reagent is dispensed in a diluent in the lower chamber, and test red blood cells are placed in the reaction upper chamber. The reaction vessel is then centrifuged. The centrifuging accelerates the reaction, if any, between the reagent and the blood cells, and also urges any cells toward the bottom of the columns. The glass beads or gel in the lower chamber act as a filter, however, and resist or impede downward movement of the particles in the column. As a result, the nature and distribution of the particles in the lower chamber after centrifuging provides a visual indication of whether any agglutination reaction occurred in the lower chamber, and if so, of the strength of that reaction.
A disadvantage of the “index card” lies in the difficulty in automating the testing procedure described above. Conventional blood analysis systems include a multitude of stations or assemblies, each of which performs one or more functions, and typically a significant amount of operator supervision and labor is needed to operate the systems. For instance, the index card must be moved from a first station to a second station in order to perform the introduction of fluids into the reaction vessel and perform centrifugation. A complex and expensive equipment is then required as well as significant operator time, care and skill to insure that each station operates properly.
Document U.S. Pat. No. 4,226,531 discloses a disposable multi-cuvette rotor for use in an analytical photometer where each cuvette is divided into adjoining sample and reagent/measuring chambers by a wedge-shaped element and reactants are transferred by centrifugal force from one chamber to the other (see also U.S. Pat. No. 5,266,268).
Document U.S. Pat. No. 4,244,694 discloses a reactor/separator device for use in solid phase immunoassays and comprising a column which is open at both ends, a retaining and filtering means disposed in said column and which is permeable to aqueous solutions when subjected to a centrifugal force, a reaction and separation chamber disposed in said column above said filtering means and containing at least one matrix having immobilized therein an antigen or antibody component for the separation of at least one of said components of an antigen-antibody system.
Document EP1450159 discloses an apparatus for conducting an agglutination assay comprising a first section for receiving a fluid and a second section for receiving the fluid of the first section upon application of a centrifugal force. The first and sections are disposed fixedly and horizontally on a rotating support.
Document U.S. Pat. No. 5,869,347 discloses a method of detecting an analyte in a test liquid by agglutination in a reaction vessel which contains a single compact, porous matrix and which, following the action of gravitational forces, allows qualitative or semi-quantitative determination of the agglutination reaction.
Documents U.S. Pat. No. 4,092,113, WO99/21658 and U.S. Pat. No. 3,468,474 disclose a device for preparing a plasma sample comprising a tube (two concentric tubes which are releasably connected together in U.S. Pat. No. 4,092,113) that can be centrifuged to separate out plasma from the blood.
Here, in order to achieve desired analysis accuracies, the rotor must have precise and stable dimensional accuracies that are uniform between the several cuvettes of the rotor. However, these are hard to achieve since the manufacture of such multi-cuvette requires two parts to be made by injection molding and welded to one another. There is also an unacceptable tendency for reactant (reagent or sample) material to spontaneously move or “wick” along the region between the upper surface of the cuvette and the side wall of the cuvette, resulting in premature initiation of the coagulation reaction and thereby distorting the accuracy of the clot formation measurement.